Part One of Two
While most of you are probably familiar with common causes of hearing loss like old age or loud noise, many are likely unaware of the numerous genetic links and syndromes that can cause or contribute to hearing loss. Around 50 to 60 percent of hearing loss in children is caused by their genetics, while 25 percent is due to environmental causes like infections during pregnancy and complications post-birth. In the grand scheme of things, how does it all work?
Some facts about genetics
Genes form the instructional manual for your body. They tell it what your hair color will be or if you will develop freckles. Half of your genes come from your mother and the other your father. But if any of the inherited genes are mutated (defective), hearing loss is a possible outcome. It all depends on the type of chromosome that would be affected (X or Y) and whether it is dominant or recessive. Inherited hearing loss can occur at birth or at any stage in a person’s life. There are four ways these disorders can be inherited:
- Autosomal Dominant Inheritance: If you were to inherit an abnormal gene from only one parent, you can develop the trait associated with that gene, whether your parent has the actual condition or not. Since the mutated gene is dominant, you might be at risk even if your other parent’s matching gene is normal.
- Autosomal Recessive Inheritance: Two mutated genes must be inherited, one from each parent, for the disorder to develop. If both parents carry the same defective recessive gene, you have a 25 percent chance of developing the condition and becoming a carrier of both recessive genes. Alternately, you have a 25 percent chance of receiving two entirely healthy genes and have no risk of developing the disorder. You also have a 50 percent chance of being a carrier even if you don’t develop the actual genetic condition.
- X-linked Inheritance: While females have two X chromosomes (one from their mother and one from their father), males only receive one X chromosome from their mother and inherit the Y chromosome from their father. If you’re and receive one mutated gene, the other X chromosome can most likely compensate since only one X needs to be active in a cell. However, because males only have one X, if you’re male and receive a mutated X gene you are likely to develop the disorder to which it’s linked.
- Mitochondrial Inheritance: Mitochondria are known the powerhouse of the cell because they are responsible for the production of energy. Like your body, mitochondria also have their own DNA. They are only found in female eggs, so cannot be carried by males. A mitochondrial condition can be passed down through maternal inheritance for generations.
Learn more about genetic hearing loss
Next week, we’ll go into more detail on the different types of genetic hearing loss and list the top ten disorders linked to it. In the meantime, it is never a bad idea to learn if you are having hearing loss symptoms. When you hear clearly, life sounds brilliant!